Myelination of the central nervous system (CNS) is a complex developmental process, requiring exquisitely timed interactions between axons and the myelin forming cells, the oligodendrocyte, and the appropriate temporal expression of an array of myelin genes. The initial elaboration of the myelin sheath in the developing CNS, and the long-term maintenance of compact myelin, each place different demands on the myelin forming cell. However, both processes are likely to be influenced by the structural and transport properties of the oligodendrocyte cytoskeleton. This proposal will study a new and unique rat myelin mutant, the taiep rat, which develops a chronic progressive neurological disease as a consequence of a CNS myelin disorder, associated with a microtubular accumulation in oligodendrocyte. The long-term goals are to characterize this mutant and its molecular defect and use it to define the role of microtubule and associated proteins in myelin formation and maintenance. To achieve these long-term goals, five specific aims have been planned: 1) The phenotype of the mutant will be characterize using morphological and morphometric approaches to study gla, cell kinetics, myelin, and the onset of the microtubule accumulation. 2) To determine whether environmental factors in the taiep CNS play any role in the development of the microtubule accumulation, cross transplantation experiments will be carried out. These will study the structure and function of taiep oligodendrocyte transplanted into the CNS of other myelin mutants, and of normal cells transplanted into the taiep CNS. 3) The polarity, stability and organizing centers of microtubule in the taiep rat oligodendrocyte will be compared to normal cells to determine whether an abnormal organization of tubules might interfere with transport events within the cell. 4) The role of microtubule regulatory proteins in the taiep mutation will be studied using antibodies to these proteins by Western blots and immunolabelling. Absence, or an over-or under- expression, or ectopic expression, of such a protein will be determined. Messenger RNAs for these proteins will also be examined by Northern blots and in situ hybridization. Finally, 5) To study the effects of accumulation of microtubule in taiep oligodendrocyte, cultures of these cells will be immunolabelled for myelin proteins known to co-localize with the cytoskeleton, and myelin protein mRNAs will be localized by in situ hybridization. Similar experiments will be performed on normal oligodendrocyte in which the cytoskeleton has been pharmacologically manipulated.